KR20000023552A - CDMA Power control for paging and initial traffic channel power - Google Patents

Abstract

PURPOSE: A CDMA power control method for paging and initial traffic channel power is provided to dynamically determine optimum initial channel power in accordance with present forward link loading and the strength of received pilot signals. CONSTITUTION: A CDMA power control method for paging and initial traffic channel power comprises a step transferring a pilot signal to a mobile station of a telecommunication system, a step determining optimum paging channel power in accordance with the strength of the received pilot signal, and a step transferring a paging message to the mobile station through a paging channel in the optimum paging channel power. The determination step further comprises a step determining optimum paging channel power in accordance with the strength of the pilot signal and forward loading being the ratio of present transfer power to maximum transfer power.

Description

CDMA Power control for paging and initial traffic channel power

The present invention relates to CDMA power control for dynamically determining optimal paging and initial traffic channel power to reduce call origination failure in a mobile communication system.

Typically, when a mobile station fails to receive a base station (BS) grant signal, a channel assignment message (CAM), a forward grant (FW) signal, or a service connection (SC) message, conventional code division multiple access (CDMA) mobile communications. A call initiation failure occurs in the system. Table 1 lists the failure rates of each of the aforementioned call initiation failures. BS acknowledgment failure (34.3% failure rate) is the main reason for call initiation failure. BS grant failures occur when the mobile station sends an access probe to the base station to request a connection from the mobile communication system and the forward paging channel power from the base station to the mobile station is insufficient and is not received at the base station.

No BS ACK No CAM No FW ACK NO SC Etc % Failure 34.38 9.38 31.25 20.31 4.69

IS-95-B is a mobile station-base station compatibility standard for dual-mode wide band spread spectrum. When the mobile station loses a paging channel, the access attempt handoff is in IS-95-B to improve call initiation failure by performing a handoff to another paging channel. However, an access attempt handoff cannot basically resolve a base station grant failure. For example, an access attempt handoff only determines which paging channel to exchange, and therefore does not adjust paging channel power. When the forward link power of the paging channel is insufficient, the access attempt handoff fails.

In general, base station acknowledgment can be taken by increasing paging channel power. Currently, the average digital gain unit (DGU) for the traffic channel is in the range of 67-75 and the constant DGU setting for the paging channel is 64. Table 2 lists the call initiation failure rates derived from the field test results for the baseline case with paging channel DGU = 64, initial traffic channel DGU = 80, T50m = 0.2 seconds and T51m = 1.0 second. In that example, a time limit of T51m = 1.0 second is set for the mobile station reporting the receipt of two good traffic channel trames transmitted from the base station to the base station. After the first good traffic channel frame, the second good traffic channel frame must be received within a time limit of T50m = 0.2 seconds. After the mobile station has been tuned to a particular traffic channel, the call is dropped if an acknowledgment report of two good traffic channel frames is not sent to the base station within T51m = 1.0 seconds. In the case of the baseline, 13.03% of all calls are failures, 4.48% of all calls are failures for base station admission failures, which is 34.38% of all failed calls.

Occation Actual failure rate No BS ACK% No CAM% No FW ACK% NO SC% Etc% 0 Baseline 13.03 (100) 4.48 (34.38) 1.22 (9.38) 4.07 (31.25) 2.65 (20.31) 0.61 (4.69) One PG DGU = 90 Traffic DGU = 108 13.38 (100) 2.12 (15.87) 1.06 (7.94) 7.86 (58.73) 1.70 (12.70) 0.64 (4.76) 2 T50m = 1 secT51m = 2.8sec 10.14 (100) 3.86 (38.10) 0.97 (9.52) 0.72 (7.14) 2.66 (26.19) 1.93 (19.05) 3 PG DGU-90 Traffic DGU = 108T50m = 1secT51m = 2.8sec 7.26 (100) 1.21 (16.67) 0.4 (5.56) 2.42 (33.33) 3.02 (41.67) 0.02 (2.78)

In comparing the baseline case and identifying the difference from the aspect of case 1, the test results in Table 2 show that the base station admission failure rate is improved by an increased paging channel DGU greater than 50%. However, increased paging channel power may negatively affect mobile communication system capacity by system power budget. When more power is allocated to the paging channel, less power is available to the traffic channel. In addition, system noise increases as paging channel power increases, which contributes to increased interference. Further discerning the difference from case 1, the increased paging channel power reduces the base station admission failure rate, but the forward signal admission failure rate increases significantly with increasing user interference. This results in a reduction of about 2.5 forward link users. To mitigate this negative impact, the T50m and T51m time limits can be increased as in Case 2, and the base station admission failure rate can be improved. However, this approach is not practical because the mobile unit must be serviced to change the T50m and T51m time limits.

1 illustrates a mobile communication system of a preferred embodiment of the present application.

FIG. 2 shows the base station 30 of FIG. 1 in more detail.

3 shows the message exchange station 40 of FIG. 1 in more detail.

Explanation of symbols on the main parts of the drawings

10: mobile station 30: base station

40: mobile switching center 50: public switched telephone network

301: antenna 303: transceiver

403: controller 405: memory

In the present invention, the paging channel power and initial traffic channel power are determined according to the current RF state, and are set dynamically, so that when the RF state is bad, the channel power can increase, and when the RF state is good, the channel power decreases. can do. The present invention determines the optimal paging channel power and initial traffic channel power according to the current forward link loading of the base station and the pilot signal strength of the pilot signal received at the mobile station. The base station then sends a paging message or call to the mobile station over the traffic channel and paging channel at the determined optimal initial traffic channel power and the determined optimal paging channel power.

1 illustrates a CDMA mobile communication system as a preferred embodiment of the present application. As illustrated in FIG. 1, a mobile communication system includes a number of base stations 30, 31, and 32 that transmit and receive communication signals to / from mobile station 10. Although not illustrated, each base station may include a respective sector. The mobile switching center 40 is coupled to a plurality of base stations 30-32 via a communication line L, and to enable communication between the mobile station 10 and other parts of the PSTN 50 to a public switched telephone network (PSTN). More combined with). Although three respective base stations are illustrated, the mobile communication system may include any base stations.

2 illustrates base station 30 in more detail. Transceiver 303 transmits and receives RF signals to and from mobile station 10 via antenna 301. The transceiver 303 and antenna 301 may be conventional transceivers and antennas, and may operate in a conventional dual communication mode that enables the transmission and reception of RF signals. Alternatively, the transceiver 303 may be replaced with a separate transmitter and receiver pair, and the antenna 301 may include a transmit antenna and a receive antenna. The transceiver 303 is demodulated, the filter RF signal is received from the mobile station 10 via an antenna 301, and provides a corresponding demodulation received signal to the controller 305. In addition, the transceiver 303 is modulated, amplifies the transmission signal provided from the controller 305, and provides the modulated transmission signal to the antenna 301 for transmission to the mobile station 10 as an RF signal.

The base station 30 includes a transceiver 309 that transmits and receives signals to and from the mobile switching center 40 via the communication line L. The transceiver 309 may be a conventional transceiver known by one of the common techniques. In an alternative embodiment, the transceiver 309 may have a transmitter and receiver pair for transmitting and receiving signals to and from the message exchange 40 over a pair of communication lines (L).

The operation of the base station 30 is controlled by the controller 305 in the manner described below. The controller 305 may be a microprocessor that controls the operation of the base station 30 in accordance with software programming stored in the memory 307. As will be readily understood by one of the general techniques, alternatively, the controller 305 may include various discrete hardware circuit components and should not necessarily be limited to be based on a microprocessor. Further, in addition to storing an operating program for the base station 30, the memory 307 includes a working memory that can be used by the controller 305.

3 illustrates the mobile switching center 40 in more detail. The transceiver 401 is coupled to a communication line L for receiving and transmitting signals to and from base stations 30-32. The transceiver 401 may be a conventional transceiver used in a mobile switching center, which is understood as one of general techniques. In alternative embodiments, the transceiver 401 may have a transmitter and receiver pair for transmitting and receiving signals individually over a pair of communication lines (L). The operation of the mobile switching center 40 is controlled by the controller 403 as described in more detail below. The controller 403 may be based on a microprocessor and may operate to control the operation of the mobile switching center 40 in accordance with software programming stored in the memory 405. The memory 405 can also include a working memory area that can be used by the controller 403. The controller 403 is also coupled to the PSTN 50.

Operation according to a preferred embodiment of the present application will be described with reference to Figs. The following notation will be used throughout the description. Ec / Io is the pilot signal strength or pilot power of the pilot signal received at the mobile station. L_F is the current forward link loading of the base station in the desired sector. The current forward link loading is derived from the ratio of the base station's current transmit power to the base station's maximum transmit power. L_F may be determined by the controller 305 of the base station 30 based on the Ec / Io of the pilot signal reported by the base station. Typically, the maximum transmit power of the base station is 8 watts. T pilot is the pilot power transmitted from the base station of the desired sector and is generally set to 15-20% of the maximum transmit power of the base station. F_pilot is a fraction of the transmitted pilot power of the base station's maximum transmitted power, typically 15%. P_pilot is the received pilot power at the mobile station. (Eb / No) p is the required quality of the paging channel or, in other words, the required bit energy level of the paging channel. (Eb / No) t is the required quality of the traffic channel or, in other words, the required bit energy level of the traffic channel. In general, (Eb / No) p and (Eb / No) t are set to 7 dB, but if desired, may be set to approximately 9 dB. It is understood that the values given above are by way of example and can be set as desired and therefore no limitations should be considered.

In the preferred embodiment, the mobile station 10 of FIG. 1 locks on with the strongest pilot signal and generates a pilot measurement message (PSMM) that confirms the received pilot signal and pilot signal strength (Ec / No). Let's do it. For example, as tracked on a pilot signal from base station 30, mobile station 10 transmits a PSMM to base station 30. The controller 305 of the base station 30 then determines the optimal paging channel power and initial traffic channel power according to the software programming stored in the memory 307 based on the reported pilot signal strength and the current forward link loading. The interference ratio of the internal interference occurs within the desired sector or cell, and the external interference is created by other cells plus noise, and assumes a known or easily induced element (O) The required quality (Eb / No) p and (Eb / No) t are used to determine the optimal paging channel power and initial traffic channel power at a specific time, such as:

Specifically, the pilot signal strength reported by the mobile can be expressed as follows:

Here, I_in and I_out are internal interference and external interference, respectively, and include thermal interference. The inverse of the pilot signal strength can be expressed as follows:

Since the pilot power is a fixed percentage of the total maximum output power of the base station 30, the internal interference ratio of the pilot power received at the mobile station 10 can be expressed as follows:

Substituting Equation 3 into Equation 2 is as follows:

From Equation 4, since I_out = P_pilot x A, the ratio of the external interference to the internal interference of the other cell plus noise can be expressed as follows:

The required received paging channel power p_page can be expressed as target quality (Eb / No) p as follows:

Where O is an orthogonal factor for internal interference. Since welsh codes are used in CDMA mobile communication systems, the channels of each sector are orthogonal and thus do not interfere with each other during demodulation. However, multipath signals from a single source exist in a CDMA mobile communication system. Although the multipath signal is transmitted at the same time, it may not be received at the mobile station at the same time because of the time delay caused by reflection from the subject. Thus, the corresponding received channel may not be exactly orthogonal, thus increasing internal interference. Orthogonal elements provide a measure of internal interference due to multipath. Typically, the orthogonal element can be set to 0.1 or 0.2.

Equations 6 and 7 represent the required quality (Eb / No) p of the paging channel and the received paging channel power P_page needed for internal and external interference. Since the propagation loss between the base station and the mobile station in the given instance is the same, the ratio of the required received paging channel power (p_page) for the internal interference (I_in) that occurs within the sector is the current transmitted power (T_in) occurring within the sector. Equal to the required transmitted paging channel power T_page.

Therefore, the necessary transmission paging channel power T_page can be solved by substituting Equation 6 into Equation 7,

From Equation 5, I_out can be expressed as follows:

Substituting Equation 9 into Equation 8 gives:

If you rearrange it,

T_in can be expressed as:

Substituting Equation 11 into Equation 12, the required transmitted paging channel power, or T_page, which is the optimal initial paging channel power, can finally be expressed as:

Since all values of Equation 13 determine or are known the pilot signal strength of the pilot signal reported by the mobile station, the required transmitted paging channel power for the corresponding RF and forwarding loading state can be determined by the controller 305. have. Controller 305 then controls transceiver 303 to transmit the corresponding paging message over the paging channel to mobile station 10 via antenna 301 at the required transmitted paging channel power. Because the optimal paging channel power is dynamically determined according to the current RF state, the paging channel power can only be increased to the extent necessary when needed. Similarly, paging channel power may be reduced when RF conditions are allowed. Thus, the system power budget is effectively allocated and the interference generated is minimized.

In a more preferred embodiment, the optimal paging channel power is determined by the controller 403 of the mobile switching center 40 according to the software stored in the memory 405. In such an embodiment, the PSMM is generated by the mobile station 10 and transmitted to the base station 30. The base station 30 then sends the PSMM to the mobile switching center 40 via line L. Thereafter, the controller 403 sends the base station 30 to the base station 30 based on the PSMM and the current forward link loading of the base station 30 determined based on the reported pilot signal strength according to Equation 13 described in the first embodiment. Determine the required transmitted paging channel power for Controller 403 then controls transceiver 401 to send information to base station 30 indicative of the required transmitted paging channel power. Then, it sends a paging message to the mobile station 10 over the paging channel at the required transmitted paging channel power. An advantage of this embodiment is that the paging channel power can be controlled and set by the mobile switching center 40 without base station software and resources.

In still other embodiments, the optimal initial traffic channel power may be determined according to the pilot signal strength reported from the mobile station as follows.

Equation 14 is identical to Equation 13 except that the required quality (Eb / No) t of the traffic channel is used in Equation 14 instead of the required quality of the paging channel (Eb / No) p of Equation 13. Do. According to the first and second embodiments, the required traffic channel power may be determined at the base station 30 or at the mobile switching center 40.

The necessary programming for processing the processing described in accordance with the above-described embodiments is not limited to being stored in the memories 307 and 405 of the base station 30 and the mobile switching center 40 of Figs. The programming can be recorded by a controller 305 and 403 of the base station 30 and the mobile switching center 40 respectively in a computer readable medium such as a floppy disk or CD ROM read. Alternatively, programming may be sent from the mobile switching center 40 to the controller 305 of the base station 30 via a transfer signal along line L.

Further, power control for paging channel power and initial traffic channel power is not necessarily limited in terms of corresponding figures, explanatory example values. For example, the values of the maximum transmit power, T_pilot, F_pilot (Ec / No) t, (Ec / No) p, and orthogonal element O may be preset by the service provider, and are in memory 307 and 405. Can be stored. Further, although the controller 305 of the base station 30 and the controller 403 of the mobile switching center 40 are described based on a microprocessor operating in accordance with respective software programming stored in the memories 307 and 305, Controllers 405 and 403 may be discrete circuit components including multipliers and adders or logic gate arrays. In addition, the controllers 305 and 403 may be integrated memories in which the memories 307 and 405 of FIGS. 2 and 3 are not necessary. In addition, as described, initial paging channel control and power control of initial traffic channel power are not necessarily limited to CDMA systems, but may be appropriately applied to mobile communication systems.

Code division multiple access power control for paging channel power and initial traffic channel power dynamically determines the optimal initial channel power according to the current forward link loading of the desired sector and the pilot signal strength of the pilot signal received at the mobile station. The initial paging channel power and the initial traffic channel power may be determined at either the base station or mobile switching center of the mobile communication system.

Claims (26)

In the base station of the mobile communication system, A transmitter for wirelessly transmitting a pilot signal and a paging message to a mobile station of a mobile communication system; A controller for determining an optimal paging channel power according to pilot signal strength of the pilot signal wirelessly received by the mobile station; And the transmitter wirelessly transmits the paging message to the mobile station over a paging channel at the optimum paging channel power. The method of claim 1, The controller determines an optimal paging channel power according to the pilot signal strength and forward loading of the base station, The forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 1, Wherein the controller determines an optimal initial traffic channel power in accordance with the pilot signal strength. The method of claim 1, And the mobile communication system is a CDMA mobile communication system. A mobile switching center of a mobile communication system to which an indication indicating pilot signal strength of a pilot signal wirelessly received by a mobile station of a mobile communication system is supplied, And a controller for determining an optimal paging channel power for wireless transmission of a paging message to the mobile station according to the pilot signal strength of the pilot signal. The method of claim 5, The controller supplies information indicative of the optimal paging channel power to a base station of a mobile communication system, And the paging message is wirelessly transmitted from the base station to the mobile station at the optimum paging channel power. The method of claim 6, The controller determines the optimal paging channel power according to the pilot signal strength and forward loading of the base station, And the forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 5, And the controller determines an optimal initial traffic channel power in accordance with the pilot signal strength. The method of claim 5, And the mobile communication system is a CDMA mobile communication system. In the method for controlling the transmission power of the base station of the mobile communication system, Wirelessly transmitting the pilot signal to a mobile station of the mobile communication system; Determining an optimal paging channel power according to pilot signal strength of the pilot signal wirelessly received by the mobile station; Wirelessly transmitting a paging message to the mobile station over a paging channel at the optimum paging channel power. The method of claim 10, The determining step includes determining an optimal paging channel power according to the pilot signal strength and forward loading of the base station, And said forward loading of said base station is a ratio of the current transmit power of said base station to the maximum transmit power of said base station. The method of claim 10, And the base station controls the transmit power of the base station of the mobile communication system to determine the optimal paging channel power. The method of claim 10, And the mobile switching center of the mobile communication system controls the transmit power of the base station of the mobile communication system to determine an optimal paging channel power. The method of claim 10, Determining an optimal initial traffic channel power in accordance with the pilot signal strength; Wirelessly transmitting a call to the mobile station over a traffic channel at the optimal initial traffic channel power. The method of claim 10, And the mobile communication system is a CDMA mobile communication system. An article of manufacture in the form of a computer-readable medium for controlling the transmit power of a base station in a mobile communication system, A pilot source code segment for causing a computer in the base station to wirelessly transmit a pilot signal to a mobile station in a mobile communication system; A paging channel determiner code segment for causing the computer to determine an optimal paging channel power according to the pilot signal strength of the pilot signal wirelessly received by the mobile station; And a paging source code segment for causing the computer to wirelessly transmit a paging message to the mobile station over a paging channel at the optimal paging channel power. The method of claim 16, The paging channel determiner code segment allows the computer to determine the optimal paging channel power according to the pilot signal strength and forward loading of the base station; The forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 16, A traffic channel determiner code segment for causing the computer to determine an optimal initial traffic channel power according to the pilot signal strength; Further comprising a traffic channel source code segment for causing the computer to wirelessly transmit a call to the mobile station over a traffic channel at the optimal initial traffic channel power. The method of claim 16, An article of manufacture controlling the transmit power of the base station in a CDMA mobile communication system. An article of manufacture in the form of a computer readable medium for controlling the transmit power of a base station of a mobile communication system, A paging channel determiner code segment for causing a computer of a mobile switching center of the mobile communication system to determine an optimal paging channel power according to the pilot signal strength of a pilot signal wirelessly received by the mobile station of the mobile communication system; And a paging channel source code segment for controlling the base station to wirelessly transmit a paging message to the mobile station over a paging channel at the optimum paging channel power. The method of claim 20, The paging channel determiner code segment allows a computer to determine the optimal paging channel power according to the pilot signal strength and forwarding loading of the base station; The forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 20, A traffic channel determiner code segment for causing the computer to determine an optimal initial traffic channel power according to the pilot signal strength of a pilot signal; And a traffic channel source code segment for controlling the base station to wirelessly transmit a call to the mobile station over a traffic channel at the optimal initial traffic channel power. The method of claim 20, A product for controlling transmit power in a CDMA mobile communication system. In the transmission signal given to the carrier to control the transmission power of the base station of the mobile communication system, A pilot source code segment for causing a computer in the base station to wirelessly transmit a pilot signal to a mobile station in a mobile communication system; A paging channel determiner code segment for causing the computer to determine an optimal paging channel power according to the pilot signal strength of the pilot signal wirelessly received by the mobile station; A paging source code segment for causing the computer to wirelessly transmit a paging message to the mobile station over a paging channel at the optimal paging channel power. The method of claim 24, The paging channel determiner code segment allows a computer to determine the optimal paging channel power according to the pilot signal strength and forward loading of the base station, The forward loading of the base station is a ratio of the current transmit power of the base station to the maximum transmit power of the base station. The method of claim 24, A traffic channel determiner code segment for causing the computer to determine an optimal initial traffic channel power according to the pilot signal strength; And a traffic channel source code segment for causing the computer to wirelessly transmit a call to the mobile station over a traffic channel at the optimal initial traffic channel power.